The invention proceeds from an elongate light source in accordance with the preamble of claim 1.
Such light sources are used, for example, in combination with an optical conductor plate for the purpose of back lighting displays, in particular liquid crystal displays (LCDs), but also large-area billboards.
For this purpose, the light of the elongate light source is launched into the optical conductor plate (so-called edge-light technique) through at least one narrow side (edge) thereof. By means of reflection at a diffuse reflecting layer fitted on the underside of the optical conductor plate, this light passes through to the outside over the entire front side of the optical conductor plate, and thereby acts like a flat light source extended in accordance with the dimensions of the optical conductor plate.
Use is made, for example, of tubular or else curved, for example L-shaped or U-shaped fluorescent lamps, as elongate light source.
In order to increase the luminance, the elongate light sources can be provided along their longitudinal axis on the inside or outside of the lamp vessel with a reflector for visible light which is cut out over a defined region along the longitudinal axis. This creates an aperture through which the light of the lamp passes to the outside (aperture lamp).
Elongate light sources are, however, also used for general lighting as well as for decorative purposes and, increasingly, in automobile engineering, for example as a flasher light or stop light, and for interior lighting. Of particular significance for most of the said purposes of use is the possibility of adapting the elongate light source to a prescribed shape, for example the shape of a motor vehicle, for use as a motor vehicle flasher light.
Although the invention develops its advantageous effect with all elongate lamps which emit a significant proportion of their light flux through the end face of one or both lamp ends, elongate lamps based on dielectrically impeded discharges with strip-shaped electrodes have proved to be particularly advantageous. By contrast with conventional electrodes fitted at the respective end faces of the cylindrical discharge vessel, this shape of the electrodes also permits the length of the non-luminous ends to be kept to a minimum.
Such a lamp is known, for example, from DE-C 197 18 395 C1. This is a tubular aperture fluorescent lamp which has at one end a base with two connecting pins. The lamp also has parallel to the tube longitudinal axis two diametrically arranged strip-shaped electrodes, one of them on the outer wall and the other on the inner wall of the discharge vessel. The two electrodes are connected in the interior of the base to the two connecting pins. The connecting pins are, for their part, connected via electric lines to the two poles of a pulsed voltage source. The lamp is distinguished by a relatively high useful radiation efficiency.
However, the light flux emitted axially at the two lamp ends through the respective end face remains unused. Moreover, it is difficult to bend such lamps into a non-tubular, for example L shape, without influencing the electrode tracks undesirably. When bending the lamp vessel, there is the risk that the electrode tracks will become detached from the vessel wall, at least in regions of large curvature.
It is the object of the present invention to provide an elongate light source in accordance with the preamble of claim 1 which avoids the disadvantages of the prior art and which can be implemented in virtually any desired shapes and lengths in a simple way.
A further aspect of the invention is to make use, in a substantially radial direction, of the light flux emerging axially from the end faces of the elongate light source.
This object is achieved by means of the characterizing features of claim 1. Particularly advantageous refinements are to be found in the dependent claims.
Moreover, protection is gained for a lighting device having this elongate light source, in particular for back lighting LCDs.
The fundamental idea of the invention is based on the finding that in the case of elongate lamps a substantial fraction of the total light flux is coupled out in some circumstances in the axial direction from the end faces of the lamp ends. The reason for this with fluorescent lamps is to be seen in that owing to the fluorescent coating or, with aperture lamps, to the reflector coating the tubular discharge vessel acts like a tubular optical conductor (light pipe) which guides the light along the tube axis. This effect occurs in a particularly pronounced fashion with the elongate lamps, mentioned at the beginning, based on dielectrically impeded discharges and having strip-shaped electrodes. By contrast with elongate lamps with electrodes arranged conventionally in an axial fashion at the two ends of the tubular discharge vessel, for example incandescent filaments or cold cathodes, it is possible, specifically, for the lightxe2x80x94in the case considered herexe2x80x94to leave the discharge vessel axially through the ends in a substantially unimpeded fashion.
The invention now proposes an elongate light source having at least one elongate lamp with two ends which has a light-guiding element at at least one end.
The function of such a light-guiding element consists essentially in at least largely picking up the light passing through the relevant end of the lamp during operation of the lamp, and in re-emitting it in a suitable spatial distribution for the targeted lighting purpose.
The or each light-guiding element consists of a transparent non-conducting plastic material, for example acrylic glass. The elements can thereby be produced relatively cost-effectively, for example using injection molding technology.
In one embodiment, a light-guiding element is provided with a depression for holding a lamp. In this way, the light-guiding element picks up the light emerging through the lamp end and emits it outwards in a preferably radial fashion by means of scattering inside the light-guiding element. The light losses during passage through the optical conductor are negligible in this case.
The surface of the light-guiding element is suitably shaped in order to influence the spatial emission characteristic. Thus, the surface can be matted in order to achieve a virtually Lambertian light distribution in all spatial directions, such as fluorescent lamps also have. Another possibility consists in silvering all the surfaces, with the exception of the depression for light launching and a narrow, matted strip for light outcoupling (aperture), for example by vacuum deposition with aluminum or bonding with a reflecting film. If the light strikes the non-silvered surface of the element, it is coupled out. If it strikes a reflecting surface, it is reflected back into the light-guiding element. This happens until it strikes the exit surface (aperture) and can leave the element. In this way, the light-guiding element appears bright, as if the light were generated therein. The matting is preferably to be employed in the case of the use of fluorescent lamps, the silvering, by contrast, chiefly in the case of aperture fluorescent lamps.
In a development, the light-guiding element additionally functions as a base. Moreover, it is also provided that the light-guiding element base has terminals for connecting to an electric ballast. For the purpose of supply using an electric ballast, the terminals are connected to the electrodes. In the case of a lamp with a base at both ends, it is generally sufficient when only one of the two bases has terminals.
If the lamp is used in conjunction with an optical conductor plate, for example for back lighting LCDs, the at least one light-conducting element has a bevel which encloses with the lamp longitudinal axis an angle typically in the range between approximately 30xc2x0 and 60xc2x0, preferably between approximately 40xc2x0 and 50xc2x0, with particular preference approximately 45xc2x0. As a result, the light emitted from the lamp in the axial direction is directed by internal reflection in the direction of the edge of the optical conductor plate and launched into the latter without high losses.
In this way, a lamp can be used which is shorter than the corresponding optical conductor plate. This also prevents either the base elements from projecting beyond the optical conductor plate or the optical conductor plate from appearing dark at its corners. Moreover, the use of the light emitted in the axial direction improves the total efficiency of the launching of the light.
In a further embodiment, the light-guiding element additionally functions as a coupler for at least two lamps. For this purpose, the light-guiding element has at least two depressions which are at a defined angle to one another and which each hold one end of the lamps. Moreover, the coupling elements contain electric contacts which permit the individual lamps to be connected electrically to one another. Since the couplers are relatively bright owing to the light-guiding effect explained above, the impression is of a continuous row of luminaires. Moreover, the row of luminaires can be shaped substantially freely by suitable selection of the angle between the depressions for the lamp ends, for example as an xe2x80x9cLxe2x80x9d or xe2x80x9cVxe2x80x9d etc. More complex shapes, for example arcs and the like, can also be at least approximated with the aid of a plurality of lamps. Thus, a light-guiding element coupler has exactly four functions: 1. mechanical holding of the lamps, 2. shaping of the light source, 3. electric connection of the lamps, and 4. light guidance and the redistribution of the light emerging axially from the lamp ends.
Such quasi-continuous xe2x80x9crows of luminairexe2x80x9d consisting of two or more lamps can be implemented relatively easily with the aid of the light-guiding elements and in conjunction, for example, with the pulsed mode of operation, preferred here and described in WO94/23442, for dielectrically impeded discharges.
Specifically, the said mode of operation permits a plurality of lamps to be operated serially, or the discharges of the respective lamps to be operated in parallel. If, for example, two linear lamps of the same length are connected to one another electrically such that the cathode is connected to the cathode and the anode is connected to the anode (parallel connection), the result is a light source whose length has been simply doubled. However, this light source can be ignited and operated with the same voltage as that of the individual lamps since, according to the electrode configuration explained at the beginning, the discharge runs perpendicular to the lamp axis, and therefore the arcing distance does not change with the lamp length. It is thereby possible to operate a series of two or more lamps with a single ballast via the electric contacts at the light-conducting elements.
Of course, it is also possible to provide individual coupling elements with a cable connection to the ballast in order, for example in the case of long rows of luminaires, to use more than one ballast or, if it is more favorable, to place the ballast more in the middle of the row than at its end.
Moreover, it is also possible for curved lamps to be connected to one another with the aid of the light-guiding elements when, for example, the desired radius of curvature is small, for example in the case of a right angle, but the aim overall is to produce a more or less continuously curved shape of the row of luminaires.
It is likewise possible according to the invention to implement a flexible row of luminaires of arbitrary length. The coupling elements described are produced for this purpose from a flexible light-conducting material.
A great advantage of the invention consists consequently in being able to implement virtually any shape and length of rows of luminaires from the standardized components of light-conducting element base, light-conducting element coupler, lamp and electronic ballast. This modular concept combines high flexibility, with regard both to the length and to the shape of the light source, with cost-effective production.
Again, dark zones are avoided at the ends, that is to say the length of the light source corresponds to the total length of the lamp with base.
In a development, the light-conducting elements have holders with the aid of which the elongate light source can be mounted on a support, for example a luminaire.